Approximately 6.5 billion eggs are produced annually in the United States alone. In an industry of this size, efficient quality control and means for limiting production costs are vital. For example, a significant number (typically 10-40%) of the eggs in a given hatchery are infertile. These eggs consume space and energy within the incubator, and can also cause contamination of other eggs. Analogous inefficiencies are caused by the difficulty that while 50% of the fertilized eggs contain male chicks, which are obviously useless to a hatchery that is dedicated to raising egg-laying hens, the determination of the sex of the chick is normally not performed until the chick is hatched, at which point, male chicks are disposed of. In addition to the energy costs of incubating a useless egg to maturity, there is the problem of eliminating the male chicks after hatching. To this end, a number of non-invasive techniques have been developed for assessing the fertility and gender of unhatched avian eggs.
For example, Soh (Avian and Poultry Biology Reviews 2005, 16, 194-195) has shown that it is possible in principle to detect a fertile egg by the CO2 that is given off by the chick inside. This method suffers from the drawback that a measurement for a single egg will take on the order of 15 minutes, far too long for a commercial hatchery. MRI has been proposed as an in ovo method for sex determination; a device based on this principle was disclosed in U.S. Pat. No. 6,029,080. As with CO2 detection, the primary drawback of MRI (in addition to the high cost of the necessary equipment) is the unduly long time (ca. 5 min per egg) required to obtain a usable image.
Methods based on measuring the amount of light transmitted by an egg (in essence, automated versions of traditional egg-candling methods) are well-known in the art; see, for example, the inventions disclosed in U.S. Pat. Nos. 5,745,228, 6,373,560, 6,750,954, and 7,019,821. More sophisticated methods that measure modulation of a light signal passing through an egg due to motion (e.g. the beating heart of the developing chick) within have been disclosed in, for example, U.S. Pat. Nos. 5,173,737, 6,860,225, 7,154,594, 7,289,196, and 7,336,348. Thermographic methods that measure infrared light emitted by a live egg have served as the basis for inventions disclosed in, e.g., U.S. Pat. Nos. 4,788,427, 4,914,672, and 4,955,728. The primary disadvantage of all of these methods is that they cannot provide a reliable measure of egg fertility until at least 10 days (in most cases, more) after the egg has been settled in the incubator.
Inventions have been disclosed that use optical spectroscopic methods, that is, absorption of light as a function of its wavelength, to measure egg fertility. For example, U.S. Pat. No. 3,704,144 (hereinafter '144) discloses a method of determining egg fertility by measuring the phase relationship of a frequency-modulated beam of light (the frequency oscillates around 575 nm, where blood absorbs strongly) passing through an egg with that of the same beam that has not passed through the egg. The presence of blood in the egg will lead to inversion of the phase of the light passing through the egg. U.S. Pat. No. 4,182,571 (hereinafter '571) discloses a method of determining egg fertility by measuring the egg's absorption of light at 575, 590, and 620 nm; absorption at 575 nm is associated with blood in a fertile egg, 620 nm with an addled egg, and the absorption at 590 nm is used to calibrate the other two measurements. Typical results of these methods are shown in FIGS. 1A and 1B, respectively. The primary disadvantage of these methods is that blood does not form until about two days after the egg is settled in the incubator, so they cannot be used even in principle during the first day or two after the egg is settled in the incubator (in practice, it is unlikely that they are sufficiently sensitive to detect fertility for at least several days more). Furthermore, since they are designed to detect blood, they cannot be used for detection of gender.
U.S. Pat. No. 6,535,277 discloses a reflectance spectroscopy method for determining egg fertility. According to this method, an egg is illuminated with a continuum of light extending from 300 nm to 1100 nm, and the reflectance spectrum obtained then compared with known spectra of fertile and infertile eggs. FIG. 1C shows typical results of this method. Because this method is only able to measure gross spectral changes, it, like those disclosed in '144 and '571, is relatively insensitive, and hence cannot detect the gender of the developing chick.
A multivariate analysis method was developed by Lawrence et al. (Lawrence, K. C.; Smith, D. P.; Windham, W. R.; Heitschmidt, G. W.; Park, B. “Egg Embryo Development Detection with Hyperspectral Imaging.” Poultry Science 2006, 5, 964) for detection of egg fertility. Their method is also incapable of monitoring the embryo within the first day after the egg is settled in the incubator.
Even though a fertile egg already contains 40-60,000 cells at the moment of laying, none of the non-invasive methods yet developed can detect egg fertility that early. Thus, a non-invasive in ovo method for detecting avian egg fertility on the day of laying that can also detect the gender of the chick remains a long-felt need.